Bacteria living in surface attached structures known as biofilms play a central role in human infection and facilitate many important processes in the environment. In this paper, we show that single attached cells can sense chemical gradients and use this information guide their movement along surfaces using tiny grappling hooks called pili. This ability allows cells to move to greener pastures, where food is more abundant. This work sheds new light into how biofilms function and presents a new tool to manipulate them to our advantage.

In this contribution we use a combination of experiments and modeling to demonstrate that fluid acceleration can 'hijack' phytoplankton's ability to sense the direction of gravity. We find this new biophysical mechanism induces cells to swim into regions of enhanced fluid vorticity, triggering multifractal patchiness.While the magnitude of fluid acceleration only becomes comparable to gravity at very large turbulent dissipation rates, this mechanism may help understand phytoplankton population dynamics in biofuel production facilities, where turbulence is often more energetic than within natural aquatic environments.

Centimeter-scale patchiness in the distribution of marine phytoplankton increases the efficacy of many important ecological interactions by enhancing the rate at which cells encounter one another and their predators. We show that turbulent fluid motion, whose effect is customarily associated with mixing in the ocean, instead generates intense small-scale patchiness in the distribution of motile phytoplankton. This motility-driven ‘unmixing’ offers an explanation for why motile cells are often more patchily distributed than non-motile cells and provides a mechanistic framework to understand how turbulence, whose strength varies profoundly in marine environments, impacts ocean productivity.

'Thin layers' are a spectacular form of patchiness in the distribution of phytoplankton. By confining a large number of primary producers to small depth intervals, these structures act as oases for higher trophic levels in a ocean where resources are often too scarce to permit survival.

In this review article, we survey the salient features of thin layers, the mechanisms at play and mathematical techniques used to infer them in the field, and their impacts on the marine ecosystem. We argue that the time is ripe for the development of a quantitative, predictive framework to better understand their occurrence and, consequently, their ecological repercussions.

We show that gyrotactic motility within a vortical flow leads to tightly clustered aggregations of microorganisms. Two dimensionless numbers, characterizing the relative swimming speed and stability against overturning by shear, govern the coupling between motility and flow. Exploration of parameter space revealed a striking array of patchiness regimes. We find that patches form under conditions typical of small-scale marine turbulence, suggesting that this mechanism may be responsible for observed microscale heterogeneity in the distribution of phytoplankton.

The growth of microbial cultures in the laboratory is often informally assessed with a quick flick of the wrist: dense suspensions of microorganisms produce translucent ‘swirls’ when agitated. Here, we rationalize the mechanism behind this phenomenon and show that the same process may affect the propagation of light through the upper ocean.

In this perspective article, we comment on the implications of a recent article by Polin et al. that foundthe phytoplankton Chlamydomonas reinhardtii can actively synchronize and desynchronize its flagella to swim in a "run and tumble" manner reminiscent of the enteric bacteria E. coli. We suggest this movement behavior might be a strategy to reduce predator encounter rates.

In this paper we demonstrate that thin layers of phytoplankton can be generated by a coupling between motility, cell morphology, and hydrodynamic shear; a process we call 'gyrotactic trapping.' Using a suite of physical experiments and modeling, we show that the vertical motility of phytoplankton is inhibited in regions of enhanced shear and leads to dense aggregations of phytoplankton.